whats right size convertor for combo?

[wedge542]

ok racers,heres the deal,how do you know whats right size 8-9-10 convertor for your combo,im looking for real experience cause i can call all the makers of top names and they will want to sell me this for this reason but im wanting real users experience,i have a daytona 2850lbs,572 indy enderle alky inj 1k hp,glide,9" 4.29,33"tire,1/8 mile,blah blah but even with no sizes to work with how would you know how to get right size without someone on phone telling you,and whats your preference with manufactures,i know i can call this one and that one but whats a true formula to find right size,not right stahl but a 8" 9" or 10".thanks